Justification:
This species grows more slowly and lives longer than other tuna species of similar size. Coupled with their restricted neritic distribution, Longtail Tuna may be vulnerable to overexploitation by fisheries. Worldwide landings have been rapidly increasing, but there is no effort information or stock assessments. It is listed as Data Deficient. More information is needed on the status of this species population, including better catch data and effort information. Management of this species also needs to be included under a fisheries management organization.

There are no known stock assessments for this species. FAO reported worldwide landings show a gradual increase from 600 tonnes in 1950 to 250,030 tonnes in 2006 (FAO 2009). There is no effort information for this species. In recent years, the countries attributed with the highest catches of longtail tuna are Indonesia, Iran, Oman, Yemen and Pakistan (IOTC 2006).

This species is pelagic and oceanodromous. It is a predominantly neritic species avoiding very turbid waters and areas with reduced salinity such as estuaries. It may form schools of varying size. It feeds on a variety of fishes, cephalopods, and crustaceans, particularly stomatopod larvae and prawns.

Maximum size is about 130 cm fork length (FL), and longevity at least five years. The smallest mature female in Thailand was 43 cm (FL), although fifty percent of females in the Gulf of Thailand were mature at 39.6 cm (FL). Fecundity of fish ranging in size from 43.8–49.1 cm varies from 1.2–1.9 million eggs (Collette and Nauen 1983, Yesaki 1994, Collette 2010). In Australia, longevity is estimated to be about 10 years (Wilson 1981), and age at first maturity in Thailand is estimated to be two years (Boonragsa 1987). This species may live as long as 18 years in the central Indo-Pacific (Grifiths et al. 2009).

This species probably spawns more than once a year, perhaps in two spawning seasons in the Gulf of Thailand. Spawning of this species is reported to be confined to coastal waters, based on the occurrence of their larvae which were collected at surface water temperatures of 28°C (Nishikawa and Ueyanagi 1991). It appears there are two distinct spawning seasons for this species off the west coast of Thailand: a major spawning period during the northeast monsoon from January to April and a minor spawning period during the southwest monsoon in August-September. Spawning is also apparently seasonal for this species off Papua New Guinea and off New South Wales, occurring during the austral summer (Yesaki 1994).

Maximum size is 130 cm FL. The all-tackle game fish record is of a 35.9 kg fish caught off Montague Island, New South Wales, Australia in 1982 (IGFA 2011).

There are two major fishing grounds for Longtail Tuna, one off the South China Sea coast of Thailand and Malaysia and the other off countries bordering the North Arabian Sea. Longtail tuna is caught mainly by gillnet and in a lesser extent by artisanal purse seiners.This species is caught in the recreational fishery in Australia, and is caught as bycatch in trawling. Most of the global catch is taken in the western Indian Ocean. Catch of this species is increasing in many areas but landings are frequently confused with Yellowfin Tuna in some regions.

This species grows more slowly and live longer than other tuna species of similar size. Coupled with their restricted neritic distribution, longtail tuna may be vulnerable to overexploitation by fisheries, and caution needs to be exercised in managing the species until more reliable biological and catch data are collected to assess the status of the population (Griffiths et al. 2009).

There are no known conservation measures for this species. More research is needed to determine the impact of fisheries on this species population, including better catch and effort information, and more comprehensive stock assessments.